This research is designed to obtain detailed information about the molecular structure of pituitary growth hormone and prolactin and the genetically related hormone of the placenta, placental lactogen, which possesses both somatotropic and lactogenic activity. A second primary objective is to determine relationships between structure and biological activity in this group of hormones in order to elucidate the molecular bases for information transfer hormone to target cell. To expand our knowledge of primary structure essential for investigation of structure/ function relationships, major effort is directed towards isolation characterization of subprimate growth hormones. Data on primary structure will be utilized in the examination of homology and evolutionary relationships among growth hormone, prolactin, and placental lactogen of other species and to search for potential homologies with other hormonal or non-hormonal proteins. In collaborative studies, the biological activity of fragments of growth hormone, prolactin, and placental lactogen produced by specific chemical or enzymatic cleavage of the native molecule will continue to be evaluated in our attempt to define the area or areas of these molecules which are responsible for binding to target cells or which constitute active sites or centers. In our laboratory, use will be made of lactogenic and somatotropic radio receptor assays as an index of biological specificiy and activity in mammary glands, liver, and other tissues. Studies will also be carried out on the large scale isolation and characterization of membrane receptor complexes from bovine and ovine mammary gland and other tissues. This will provide the means for continuing investigation of the structural relationships between growth and lactogenic hormone binding proteins and the molecular determinants of hormone-receptor interaction.